Coronary heart disease (CHD) is the leading cause of death in the United States, accounting for roughly 24% of all deaths. The cost of cardiovascular diseases in 1999 is estimated by the American Heart Association (AHA) at $286.5 billion. Myocardial perfusion scintigraphy is widely used in the evaluation of patients with known or suspected coronary artery disease (CAD). The extensive clinical use of stress myocardial perfusion imaging has resulted largely from its demonstrated improved diagnostic sensitivity and specificity for detection of CAD as compared with exercise electrocardiogram. However, there remains a general need for myocardial flow tracers with improved tracer kinetics.
Although several tracers are currently available for perfusion imaging, all of these tracers suffer from one or more limitations which render them less than ideal agents for assessment of cardiac perfusion (e.g., limited extraction at high flow (Tc99m-sestamibi, T1-201 Chloride) (Marshall et al., 1990), lack of ideal isotope (T1-201 chloride), high liver extraction (Tc99m-teboroxime and Tc99m-sestamibi) (Marshall et al., 1991).
Myocardial perfusion tracers are needed with: improved extraction on first pass; better linearity with true blood flow; improved detection of myocardial viability; and reduced accumulation in non cardiac tissues. Generally, radiopharmaceuticals may be used as diagnostic or therapeutic agents by virtue of the physical properties of their constituent radionuclides. Thus, their utility is not based on any pharmacologic action. Most clinically used drugs of this class are diagnostic agents incorporating a gamma-emitting nuclide which, because of physical or metabolic properties of its coordinated ligands, localizes in a specific organ after intravenous injection. The resultant images can reflect organ structure or function. In radioimaging, the radiolabel is a gamma-radiation emitting radionuclide and the radiotracer is located using a gamma-radiation detecting camera (this process is often referred to as gamma scintigraphy). The imaged site is detectable because the radiotracer is chosen either to localize at a pathological site (termed positive contrast) or, alternatively, the radiotracer is chosen specifically not to localize at such pathological sites (termed negative contrast).
Rotenone, [2R,6aS,12aS]-1,2,12,12a-tetrahydro-8,9-dimethoxy-2-(1-methylethenyl)-[1]benzopyrano[3,4-b]furo[2,3-h]benzopyran-6(6aH)-one, is a natural product of the Leguminosae plant family and has been used as an insecticide, pesticide and fish poison, and has been used in mitochondrial energy metabolism studies. Rotenone binds on the ND-1 gene product and inhibit Complex I in a reversible competitive manner resulting in the biological effect.
Rotenone has a high affinity for mitochondria. The myocardium is an organ rich in mitochrondria. Novel radiolabeled rotenone analogs that display efficient myocardial uptake and adequate myocardial retention are attractive candidates for clinical evaluation of myocardial blood flow. Rotenone is a specific, high-affinity inhibitor of Complex I (NADH:ubiquinone oxidoreductase), the proximal enzyme of the mitochondrial electron transport chain. Since rotenone inhibition defines the activity of Complex I, defects in radiotracer binding can be expected to reflect functional changes in the enzyme, and hence, abnormalities of the mitochondrial energy metabolism. The prior art rotenone radionuclides utilize a rotenone compound having the following structure:

Labeled rotenone studies have focused on brain and heart imaging (organs enriched with mitochondria) using tritium, carbon-11, fluorine-18, and iodine-125 isotopes (see VanBrocklin et al., 1994; Marshall et al., 2001; Blandini and Greenamyre, 1995; Charalambous et al., 1995; O'Neil et al., 1994; VanBrocklin et al., 1995; Kenski et al., 1999). Studies on iodine-125 labeled rotenone in isolated blood perfused rabbit heart, a unique model for evaluating myocardial imaging agents, have demonstrated extraction superior to that of Tc-99m sestamibi (0.84±0.05 compared to 0.48±0.10) (Marshall et al., 2001). It also was found to have greater net heart retention than that of Tc-99m sestamibi at 1 min (0.77±0.08 vs. 0.41±0.11) and at 26 min (0.46±0.13 vs. 0.27±0.11) and better correlation with true flow.